An electrophotographic photosensitive member having a photosensitive layer using an organic photoconductive substance (an organic electrophotographic photosensitive member) can be produced more easily than an electrophotographic photosensitive member having a photosensitive layer using an inorganic photoconductive substance (an inorganic electrophotographic photosensitive member). In addition, the organic electrophotographic photosensitive member has an advantage that it has a high degree of freedom of function design because of its diversity of material selection. Thus, the organic electrophotographic photosensitive member has been widely used in the market owing to recent rapid proliferation of laser beam printers.
An electrophotographic photosensitive member having a lamination type layer structure has gone mainstream as the photosensitive layer of the organic electrophotographic photosensitive member from the viewpoint of durability, the lamination type layer structure being obtained by laminating, from a support side, a charge-generating layer comprising a charge-generating substance and a charge-transporting layer comprising a charge-transporting substance in this order.
In many cases, a layer is arranged between the support and the charge-generating layer, which is intended for, for example, covering a defect on the surface of the support, improving adhesive property between the support and the photosensitive layer, preventing interference fringes, protecting the photosensitive layer from electrical breakdown, and preventing the injection of charge from the support into the photosensitive layer (see, for example, JP-A 58-095351 (Patent Document 1) and JP-A 02-082263 (Patent Document 2)). Hereinafter, a layer arranged between a support and a charge-generating layer is referred to as an “intermediate layer”.
The intermediate layer has the merit described above and a demerit that charge is apt to accumulate. For this reason, when images are printed (output) continuously, a large change in potential occurs, so an output image may have a problem.
For example, when an electrophotographic photosensitive member having an intermediate layer is used for an electrophotographic apparatus currently adopted widely in printers which uses a dark-area potential portion as a non-development portion and a light-area potential portion as a development portion (a so-called reversal development type), the sensitivity of a site irradiated with light at the time of the preceding printing increases owing to a reduction in light-area potential or in residual potential. Therefore, when a totally white image is output at the time of the subsequent printing, a ghost phenomenon (positive ghost) may occur, in which the preceding print portion is embossed with a black color.
In contrast, when a totally black image is output at the time of the subsequent printing when the sensitivity of a site irradiated with light at the time of the preceding printing decreases owing to an increase in light-area potential, a ghost phenomenon (negative ghost) may occur, in which the preceding print portion is embossed with a white color.
Various methods of reducing a change in potential such as an increase in residual potential or a reduction in initial potential when continuous printing is performed by using an electrophotographic photosensitive member having the intermediate layer have heretofore been proposed (see, for example, JP-A 62-269966 (Patent Document 3), JP-A 58-095744 (Patent Document 4), JP-A 04-310964 (Patent Document 5), JP-A 07-175249 (Patent Document 6), JP-A 08-328284 (Patent Document 7), JP-A 09-015889 (Patent Document 8), and JP-A 09-258468 (Patent Document 9)).
However, there may be cases involving problems such as a reduction in initial sensitivity and a reduction in chargeability. Therefore, continuous printing using the electrophotographic photosensitive member having the intermediate is susceptible to additional improvement.
In addition, demands for an electrophotographic photosensitive member have become more and more severe owing to recent trends toward high image quality and colorization. That is, an electrophotographic photosensitive member has been demanded, which shows no changes in properties due to a change in environment where the electrophotographic photosensitive member is used, and which causes no deterioration of an output image such as a change in potential or a ghost even in durable use.
In particular, in a high-temperature-and-high-humidity environment, solutions to: a reduction in dark-area potential (charging potential) or in light-area potential resulting from a reduction in resistance; a change in light-area potential due to durable use; and the promotion of a positive ghost; have been demanded.
In addition, in a low-humidity environment, solutions to: an abrupt increase in light-area potential resulting from an increase in resistance at an initial stage (about a period from a first revolution to a 500th revolution); a change in density of an output image due to such abrupt increase; and the promotion of a ghost due to durable use have also been demanded.
A method of suppressing a ghost involving adding a ghost alleviating agent to the intermediate layer has been proposed as one method of solving the above problems (see, for example, JP-A 2003-295489 (Patent Document 10) and JP-A 2003-316049 (Patent Document 11)).
However, durable use in a high-temperature-and-high-humidity environment or a low-humidity environment is still susceptible to improvement.
Further, an electrophotographic photosensitive member which allows the use of laser whose oscillation wavelength is a short wavelength (380 to 450 nm), and is adapted to high resolution has also been demanded.
[Patent Document 1] JP-A 58-095351
[Patent Document 2] JP-A 02-082263
[Patent Document 3] JP-A 62-269966
[Patent Document 4] JP-A 58-095744
[Patent Document 5] JP-A 04-310964
[Patent Document 6] JP-A 07-175249
[Patent Document 7] JP-A 08-328284
[Patent Document 8] JP-A 09-015889
[Patent Document 9] JP-A 09-258468
[Patent Document 10] JP-A 2003-295489
[Patent Document 11] JP-A 2003-316049